U.S. patent application number 16/286352 was filed with the patent office on 2019-09-05 for electroless plating activation.
The applicant listed for this patent is Hutchinson Technology Incorporated. Invention is credited to Kurt F. Fischer, Douglas P. Riemer.
Application Number | 20190274224 16/286352 |
Document ID | / |
Family ID | 67768860 |
Filed Date | 2019-09-05 |
United States Patent
Application |
20190274224 |
Kind Code |
A1 |
Riemer; Douglas P. ; et
al. |
September 5, 2019 |
Electroless Plating Activation
Abstract
A method of initiating and controlling electroless nickel
plating on copper substrates carried into a plating bath on a
continuous stainless steel web where the copper is electrically
bussed or in physical contact with the steel is described. A bias
current is applied to the plating bath and a feedback loop is
established to determine initiation of plating as well as to ramp
down the biasing current to prevent electro- or electroless plating
of the web.
Inventors: |
Riemer; Douglas P.;
(Waconia, MN) ; Fischer; Kurt F.; (Eau Claire,
WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hutchinson Technology Incorporated |
Hutchinson |
MN |
US |
|
|
Family ID: |
67768860 |
Appl. No.: |
16/286352 |
Filed: |
February 26, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62637238 |
Mar 1, 2018 |
|
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|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C23C 18/1671 20130101;
C23C 18/32 20130101; C23C 18/1628 20130101; C23C 18/1619 20130101;
C23C 18/1675 20130101; H05K 3/244 20130101; C23C 18/1637 20130101;
C23C 18/38 20130101; H05K 3/4661 20130101 |
International
Class: |
H05K 3/46 20060101
H05K003/46; H05K 3/24 20060101 H05K003/24; C23C 18/32 20060101
C23C018/32; C23C 18/38 20060101 C23C018/38 |
Claims
1. An electroless method of plating a metal on a substrate
comprising: providing a substrate upon which to plate a metal, the
substrate being carried by a web; introducing the web, including
the substrate upon which to plate the metal, into a plating bath;
establishing a voltage existing in said bath by placing an
electrode in contact with the bath and in contact with a roller
contacting the web outside the bath; determining a reference
voltage at which plating will initiate on the substrate; and,
applying a bias current to the web sufficient to initiate plating
only on the substrate but not on the web.
2. The method of claim 1, wherein the metal to be plated comprises
nickel.
3. The method of claim 2, wherein the substrate comprises
copper.
4. The method of claim 1, wherein the web comprises stainless
steel.
5. The method of claim 2, wherein palladium may be provided in
contact with the substrate of copper.
6. The method of claim 1, wherein the step of supplying current
controls the reference voltage.
7. The method of claim 1, wherein the substrate upon which to plate
the metal is a plurality of discrete copper traces.
8. The method of claim 1, wherein the web is continuous, but the
substrate upon which to plate the metal are discrete traces carried
by the web.
9. The method of claim 1, wherein the substrate is copper and the
web is stainless steel.
10. The method of claim 9, wherein the ratio of area of the
substrate bussed to the area of the web affects the plating on the
substrate.
11. The method of claim 1, wherein the applying of bias current is
adjusted to maintain a constant reference voltage to assure
continuous initiation of plating as the web is fed into the
bath.
12. The method of claim 1, further comprising sensing of the
reference voltage to determine plating initiation and ramping down
the bias current to prevent electro- and electroless-hybrid
plating.
13. The method of claim 4, wherein the bias current is dependent on
the state of passivation of the stainless steel web.
14. A method of electroless nickel plating only on a copper
substrate carried by a continuous stainless steel web on not on the
web itself comprising: introducing a continuous stainless steel web
into a plating bath; wherein the plating bath comprises nickel to
be plated on the substrate; arranging a continuous substrate, or a
plurality of spaced substrates, of copper bussed to the stainless
steel web; applying a bias current to the web to initiate the
nickel plating on the copper substrate.
15. The method of claim 14, further including the step of
establishing a reference voltage existing on the web in the
bath.
16. The method of claim 15, wherein the step of establishing the
reference voltage comprises placing a reference electrode in
contact with the bath containing the web near the point of entry of
the web into the bath and measuring the voltage difference with a
roller in contact with the web before it enters the bath.
17. The process of claim 14, further comprising sensing the
reference voltage to determine plating initiation and ramping down
the bias current to prevent electro- or electroless-hybrid
plating.
18. The method of claim 14, further comprising adjusting the bias
current to maintain a constant reference voltage to assure
continuous initiation of plating on the copper substrate as the web
is introduced into the bath.
19. The method of claim 14, wherein palladium is placed in contact
with the copper of the substrate.
20. A method of electroless nickel plating only on a copper
substrate carried by a continuous stainless steel web and not on
the web itself comprising: introducing a continuous stainless steel
web into a plating bath; wherein the plating bath comprises nickel
to be plated on the substrate; arranging a continuous substrate, or
a plurality of spaced substrates, of copper bussed to the stainless
steel web; establishing a voltage difference between the bath
containing the stainless steel web and the web before it enters the
bath by placing a reference electrode in contact with the bath;
applying a bias current to the web to initiate the nickel plating
on the copper substrate; sensing the voltage to determine plating
initiation; and, ramping down current to prevent electro- or
electroless-hybrid plating.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 62/637,238 filed on Mar. 1, 2018, which is hereby
incorporated by reference in its entirety.
FIELD
[0002] The present disclosure concerns mitigating the loss
reduction due to excess electroless nickel ("E-Ni") coating on a
copper substrate carried on a web of stainless steel ("SST") where
the copper is electrically bussed or in physical contact with the
steel. Prior to this disclosure, annual yield loss at an E-Ni
plater are on the order of more than US$500,000 at a production
rate of sixty rolls per week. By the use of a current controlled
reference voltage applied to the web, with an active feedback loop
to maintain the reference voltage at the level required for
electroless plating to initiate, the losses of plating on the web
are mitigated.
BACKGROUND
[0003] Electroless nickel plating is an autocatalytic process whose
initiation is the result of the catalytic activity of a given
substrate. After initiation of the plating, the process proceeds
spontaneously on the deposited-nickel layer.
[0004] E-Ni is intended to plate to copper ("Cu") traces and pads,
where a palladium ("Pd") activator can optionally be deposited on
the Cu. The Pd should act as the catalyst and activate the E-Ni
plating. From the scientific literature, "Initiation of Electroless
Nickel Plating on Copper, Palladium-Activated Copper, Gold and
Platinum", J. Flis and D. J. Duquette, J. Electrochem. Soc.:
Electrochemical Science and Technology, February 1984, pp. 254-259,
incorporated herein by reference in its entirety, a certain pattern
of voltage should be observed when plating activates. The voltage
should shift negative past the deposition voltage and then remain
at a steady-state. Some materials, such as Pd and iron ("Fe"), will
plate on their own. Most others do not, so a chemical activator is
used, here Pd. See FIG. 1 which plots the Potential, in V ("Volts")
versus SCE versus Time for Cu, Cu+Pd, Au and platinum ("Pt").
[0005] However, increased yield losses occur because of
inconsistent activation of the E-Ni plating. SST can have a
significant influence on the activation of E-Ni plating. Activation
will be dependent on part/panel design and SST processing, i.e.,
whether the SST web is passivated or not. In reel to reel plating
of a continuous web, the copper surface to be nickel plated can be
in electrical contact with the stainless steel substrate, forming a
galvanic coupling. The electrical contact can be formed by product
design, connecting the copper and stainless steel through vias in
the dielectric layer between the copper and stainless steel
surfaces. The contact between the copper and stainless steel will
generate a small voltage when the web is immersed in plating
solution, and this voltage acts as a barrier for the electroless
plating reaction. Normal deposition of palladium catalyst may not
allow initiation of the plating reaction, and an external voltage
is needed. Other factors include the relative amount or area of
copper compared to an amount or area of exposed SST through a
dielectric material. The previous surface treatment, accidental or
intentional of each of the Cu and SST also will affect plating.
When there is a problem, the Ni will only plate isolated Cu, and
none that is bussed to the SST web. Currently, there is a
significant yield loss at E-Ni plater due to activation, or lack of
activation.
SUMMARY
[0006] In a first embodiment, a current controlled reference
voltage is established to the web with an active feedback loop to
maintain the voltage at the level required for the electroless
plating to initiate.
[0007] In another embodiment, a system is employed to offset the
changing web conditions caused by bath chemistry changes, copper to
SST galvanic couple, and the state of SST passivation.
[0008] In a further embodiment, monitoring of the reference voltage
conditions in the plating bath and self-adjusting a bias current on
the web, either up or down, to maintain the desired reference
voltage.
[0009] In a still further embodiment, sensing of bias current to
determine plating initiation and ramping down current to prevent
electro- or electroless-hybrid plating.
[0010] These and other embodiments will be better understood when
read in conjunction with the detailed description of the
embodiments and the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a graphical representation which plots the
Potential, in V ("Volts") versus SCE versus Time for Cu, Cu+Pd, Au
and platinum ("Pt") according to the scientific literature ("Prior
Art");
[0012] FIG. 2 is a schematic representation of an apparatus and
method for adding a sensor to a plating module to provide reliable
plating activation feedback by voltage measurement according to an
embodiment;
[0013] FIG. 3 is a graphical representation of the electromotive
force, E, plotted against time (in sec.) up to and after manual
activation occurs according to an embodiment;
[0014] FIG. 4 is a graphical representation of ions (dashed line),
voltage (in mV) between the web and reference electrode plotted
against time (in seconds);
[0015] FIG. 5 is a schematic representation of a electroless
plating system, according to an embodiment, which has been modified
to apply current to the web via the bath while measuring web to
plating bath voltage difference for control of the plating process;
and
[0016] FIG. 6 is a graphical representation of laboratory (beaker
scale) experiments performed utilizing the present process,
according to an embodiment, in comparison to published voltage
trends with E (SHE) plotted versus time (in sec.).
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0017] As shown in FIG. 1 (Prior Art) the published scientific
literature shows a certain pattern of voltage that should be
observed when plating initiates. As shown in FIG. 1, an open
circuit potential of copper, palladium-activated copper (activation
in the solution of 1 g/L PdCl.sub.2+1 ml/L HCl for 5 sec.), gold,
and platinum after immersion into a plating solution (solid lines)
or into a supporting solution with NaH.sub.2PO.sub.2 but without
Ni.sup.2+ ions (dashed line). The voltage should shift negative
past the deposition voltage and then remain at a steady-state. Some
materials, such as Pd and Au, will plate on their own. Most others
do not.
[0018] When E-Ni is intended to plate to Cu traces and pads, a
stainless steel web is bussed to the Cu. The Cu is placed on a
stainless steel ("SST") web 10, when it is carried into and through
a plating bath. Referring to FIG. 2, it can be seen that in system
9, the SST web 10 is carried through a roller pair 11, 12 and
introduced below the surface 13 of bath 14, contained within tank
15. Insulating rollers 16, 17 carry the web 10 beneath the surface
13 of bath 14. In order to determine the voltage in the bath and in
the web, a reference electrode 18, measures the voltage difference
between roller 11 and the bath 14 contacting the SST web 10. A
current source 19 from an external rectifier 20 can be used to
manipulate the voltage to the desired value. As can be seen from
FIG. 3, electromotive force, E, is plotted against time (in sec.)
until manual activation occurs, at which time a dramatic voltage
drop occurs.
[0019] The reference electrode 18 used can be a calomel electrode,
which is mercury coated with calomel (Hg.sub.2Cl.sub.2) which is
stable at high temperature (180.degree. F.), one of the few
reference electrodes that are usable. However, the mercury
electrodes are very expensive, and contain toxic substances. It is
known to those skilled in the art that a "pseudo-reference
electrode" or "quasi-reference electrode" can be made from a piece
of platinum and is often used in non-aqueous systems (see Bard and
Faulkner, "Electrochemical Methods-Fundamentals and Applications",
John Wiley & Sons, Inc, 2.sup.nd Ed., 2001, page 53,
incorporated in its entirety by reference). Platinum, which is not
catalytically active to plating in this system, remains as a
platinum surface and works well as a reference electrode 18. The
placement of the reference electrode 18 is near to where the SST
web 10 enters the bath, rather than downstream of entry into the
bath. Located near the entrance where plating is activated, it
provides a suitable thickness control, minimizing IR drop due to
the activating current, and increases accuracy of the measurement.
The tank 15 itself is used as the anode, and it completely
surrounds the web 10. This system 9 allows us to plate specifically
on the Cu in a bi-metallic process. By holding the voltage within a
tight window, we are able to plate on one metal (e.g., Cu) and not
the other (e.g., SST). Hybrid electro- or electroless-plating is
thus prevented.
[0020] Control range is 0.2 V (200 mV).+-.0.05%. Without the use of
the reference electrode 18 in the system 9 it would be impossible
to control the voltage in such a tight window. The best that could
be achieved without the use of the disclosed system 9, including
the reference electrode and externally supplied current, would be
about 500 mV.
[0021] A voltage profile for E-Ni plater can be seen in graphical
form in FIG. 4. The voltage (in mV between the web and the
reference electrode 18) is plotted against time (in sec.). Using a
voltage controller rectifier, control over activation of plating
worked in seven of eight runs, or most of the time. Only in one
instance, was there no plating, even with assist from the
PROTECTOSTAT.TM. as we call our system 9, and in fact, showed
significantly different voltage from the predicted direction.
[0022] As shown in FIG. 5, an industrial system 50 is envisioned
wherein a web 51, carrying continuous or isolated Cu parts, enters
module 52 which comprises a series of conveying rollers 53-54,
55-56, and 57-58 to convey web 51 and its associated copper parts
through bath 59. A reference voltage is measured between points 60
and 61. The web 51, and its associated Cu parts then enters plating
module 64. Plating module 64 also comprises series of conveying
rollers 65-66, 67-68 and 69-70. Voltage is again measured between
points 62 and 63. Plating on the Cu parts occurs in plating module
64. The voltage measurements between point 62 and point 63 in the
plating bath 71 would indicate whether plating is occurring on the
Cu parts in plating module 64.
[0023] By adding a sensor to a plating module as shown in FIG. 2,
reliable activation feedback by voltage measurement can be
ascertained, as no current can flow through the sensor. Once a
current source has been added, the voltage can be manipulated to
the desired value. For various embodiments, the foregoing is
implemented in a reel-to-reel system where the web 10 can be
considered as continuous.
[0024] Although we have disclosed some embodiments, in connection
with the appended drawings, such embodiments are to be viewed as
exemplary only as one skilled in the art, to whom this disclosure
is directed, will readily envision modification and other
embodiments without the exercise of invention.
* * * * *